Toxin genes on pathogenicity islands: impact for microbial evolution

Toxin-specific genes are often located on mobile genetic elements such as p hages, plasmids and pathogenicity islands (PAIs). The uropathogenic E. coli strain 536 carries two alpha -hemolysin gene clusters, which are part of t he pathogenicity islands I-536 and II536, respectively. Using different gen etic techniques, two additional PAIs were identified in the genome of the E . coli strain 536, and it is likely that further PAIs are located on the ge nome of this strain. Pathogenicity islands are often associated with tRNA g enes. In the case of the E. coli strain 536, the PAI-associated tRNA gene l euX, which encodes a minor leucyl-tRNA, affects the expression of various v irulence traits including alpha -hemolysin production. The exact mode of ac tion of the tRNA(5)(Leu)-dependent gene expression has to be identified in the future.